Digital cellular telecommunication systems such as GSM comprise a plurality of base station subsystems (BSS), wherein a base station subsystem (BSS) typically comprises a Base station controller (BSC) and one or more Base Transceiver Stations (BTS). Each BTS provides coverage to one or more mobile stations (MS) within a certain geographic area (referred to as a cell). In order to maintain a call in progress as a MS, which is engaged in a point-to-point call or which is engaged with access to the uplink of a channel used for a voice group call, passes from one cell coverage area to another, handover of the MS from one BTS to a next BTS may be employed. Furthermore, handover may be employed to meet network management requirements, e.g. with regards to the relief of congestion in certain cells.
The handover may occur from one or more traffic channels (TCH) on one cell to one or more channels on a neighbouring cell. Alternatively, handover may occur between channels on the same cell which are carried on different frequencies. For a multiband MS, the handover may be allowed between channels on different cells which are carried on different frequency bands, e.g. between a GSM 900 traffic channel (TCH) and a DCS 1 800 TCH. For a multi-RAT (Radio Access Technology) MS, i.e. an MS supporting multiple radio access technologies such as GSM, UTRAN (UMTS Terrestrial Radio Access Network) FDD (Frequency Division Duplexing), UTRAN TDD (Time Division Duplexing), E-UTRAN (evolved UTRAN), CDMA (Code Division Multiple Access) 2000, handover may be allowed between GSM and the other radio access technologies.
The overall handover process may be implemented in the MS, BSS and MSC. Measurements of the radio subsystem downlink performance and signal levels received from neighbouring cells may be made within the MS. These measurements may be signalled to the BSS for assessment. The BSS may measure the uplink performance for the MS being served and may assess the signal level of interference on its idle traffic channels. Initial assessment of the measurements in conjunction with defined thresholds and a predefined handover strategy may be performed in the BSS. Assessment requiring measurement results from other BSS or other information resident in the network (e.g. the MSCs), may be performed in the MSC or network management components.
As such, a MS typically provides regular measurement reports to the network, e.g. via its serving BTS. These measurement reports provide information on the neighbouring cells and/or the frequencies served within the neighbouring cells. In particular, these measurement reports provide information on the downlink performance and signal levels of cells within the vicinity of the MS. A multi-RAT MS should be able to provide measurement reports comprising sufficient information on the neighbouring cells and/or the frequencies served within the neighbouring cells regarding all or some of the radio access technologies supported by the MS. At the same time, the data size of the measurement reports should be kept at a pre-determined level, i.e. the required signalling overhead for the measurement reports should be kept at or below a pre-determined level. The present document addresses this technical problem, i.e. the problem of providing measurement reports about the neighbouring cells of some or all of the supported radio access technologies to the digital cellular telecommunications system at a pre-determined limited signaling overhead.
Details regarding the handover process and the measurement reports provided by a MS are given in the document 3GPP TS 45.008 V9.4.0 Radio subsystem link control which is incorporated by reference. Particular reference is made to Section 8.4.7 of the above mentioned document, regarding additional cell reporting requirements for multi-RAT MS.